(A) Field of the Invention
The present invention relates to a single-ended sense amplifier, and more particularly, to a single-ended sense amplifier using a dynamic reference voltage and the operation method thereof.
(B) Description of the Related Art
In a conventional sense amplifier scheme, memory read operation is achieved by comparing input data with a reference voltage to determine the logic state of the input data. Hence, various types of sense amplifiers have been developed accordingly. The single-ended sense amplifier that is coupled to a single bit line is widely used in single-ended type memory designs, and can be attributed to two design styles. Many single-ended type memory designs employ an inverter as a sense amplifier. Such designs mainly use an inverter trip point as a reference voltage level. Consequently, the inverter trip point has to be carefully selected to decrease process-voltage-temperature (PVT) dependence. Reducing process-voltage-temperature (PVT) dependence, however, is not easy. Also, the inverter type sense amplifier is not suitable for large capacity memory designs due to slow bit line discharging time during read “0” operations, resulting in poor speed performance.
Another style of single-ended sense amplifier employs a differential sense amplifier with two inputs, of which one side is coupled to an input data line (bit line) and another side is coupled to a fixed reference voltage that comes from an additional reference voltage or an external voltage supply. This kind of sense amplifier design features a fast sensing speed, and is suitable for large capacity memories with proper reference voltage level adjustment and is robust enough for use in various PVT conditions. However, this sense amplifier occupies a greater area than that of the sense amplifier of an inverter type.
As shown in FIG. 1, the operation of a traditional single-ended differential sense amplifier refers to a fixed reference voltage VREF. The voltage of data line VDL decreases if the stored data is logic “0.” When VDL falls below VREF and the voltage difference ΔV between VDL and VREF exceeds a threshold value, e.g., 100 mV, the stored data will be determined as “0” and the sense amplifier will be inverted or activated. However, VDL sometimes drops very slowly, and therefore may take a long time to reach the threshold value. With high-speed performance and large memory capacity requirements, the conventional fixed reference voltage level for sensing operation cannot meet the demand. Therefore, there is a demand to expedite operation efficiency.